They left, yes. Most were not permanent residents in the first place, so they were simply returning home.

As far as giving up titles goes, that didn't/couldn't happen. The title itself belongs to the person regardless of their country of residence. Even if they choose not to use the title, it's still theirs. The law on the books from 1648 was that the person inheriting the title was ennobled whether they wanted to be or not. This actually didn't change until 1963, and even now there's just a small window of time where someone can disclaim a title immediately after inheriting it. This only lasts for the duration of their life, however. It still passes to the heir upon death.

There was only one peer in permanent residence in the American colonies - Scottish Lord of Parliament (equivalent to an English Baron) Thomas Fairfax, 6th Lord Fairfax of Cameron, from Virginia. Most of his lands were confiscated in 1779, but he personally was never bothered. He died in 1781, and his title passed to his younger brother (living in England). The family later received remuneration from the British Parliament for the lost property. Interestingly - the 7th Lord Fairfax of Cameron also died without issue, and the title then passed to a nephew, American-born Bryan Fairfax (incidentally, a good friend of George Washington). The family stayed in the US, and kept the title until the 12th Lord Fairfax moved back to the UK. Despite being American-born, the 12th Lord later served in the House of Lords as an elected Scottish Representative Peer.

The other name that comes up in the context of peers during the American revolution is William Alexander, Lord Stirling. He tried to claim the title of 6th Earl of Stirling after the 5th Earl died in 1739. The 5th Earl was his cousin through marriage. The House of Lords denied his claim. He inherited the estate, but not the peerage. He was, however, granted the courtesy style of "Lord Stirling," and he did use it, even while serving in the Continental Army.